In data transmission systems an outgoing connection is usually established by a connection code, such as a telephone number. In a conventional fixed line telephone network, each digit of a dialed number is directly transmitted to an exchange as the numbers are dialed. The dialled numbers are analyzed in the exchange, and a connection is established after the dialled number sequence is detected to be a valid, existing telephone number.
In cellular telecommunication systems a number is typically dialled on a keypad and stored in the mobile station (e.g., a cellular telephone or personal communicator). After the dialling is completed a predetermined key (i.e., the SEND key) is depressed to cause the stored number to be transmitted to the system for analysis.
Terminal equipment used in wireless local loop (WLL) networks includes a conventional telephone which can be linked to the public telephone network through a wireless transceiver unit. In many cases the transceiver unit is linked to a cellular system by radio communication.
However, as there is no SEND key available on the conventional telephone, one of the problems encountered in WLL systems has been how to decide when the dialling sequence has been completed.
One previously known solution employs a special end character to indicate the completion of dialling. By example, the end character can be a keypad character (e.g., # or *) which is normally not used for dialling. Depressing the end character key informs the WLL transceiver that dialling has been completed, and that the stored dialed number can be transmitted to a base station of the cellular system. A disadvantage of this solution is, however, that the required dialing procedure differs significantly from that used in conventional fixed networks. Some users may find such differences objectionable.
Another prior art solution has been to use time supervision. According to this approach the elapsed time starting from a last dialled digit is monitored, and after a predetermined time has elapsed (e.g., 6 seconds), the dialing sequence is assumed to have been completed. In response to the occurrence of the timeout the stored dialed sequence of digits is transmitted to the base station as the connection code.
However, one problem with time supervision is that an additional, and considerable, delay is required for the establishment of the connection. This delay is incremental to the time required by the system to actually establish the connection. This problem can be diminished by reducing the predetermined delay time. Reducing the delay time, however, can introduce other problems. For example, the called number dialing sequence may typically be interrupted by the user having to refer to a phone book or some other telephone number record. In this case a delay or pause of several seconds can easily occur between dialed digits. If such a pause in dialing is erroneously interpreted by the WLL terminal equipment as the completion of the dialing sequence, the WLL terminal equipment will transmit an incomplete telephone number to the base station, and the establishment of the connection fails. In this case the user must start the dialing procedure over, and redial the entire number.
In commonly assigned Finnish patent application FI 961330 a technique is described for setting up calls in a WLL system. In this approach the WLL equipment stores each telephone number that is successfully setup. After the number has been stored, a call made to the same number is immediately established when a newly entered number is found to equal a stored number. That is, the system is made aware of when to transmit the call setup request to the network by the newly entered number equalling a previously entered number that is known to have been successful in setting up a call.
Reference can be had to the following U.S. Patents for describing prior art WLL systems: U.S. Pat. Nos. 4,658,096, 4,737,975, 4,775,997, and 4,922,517.